astronomy

OTE Pathfinder

OTE Pathfinder is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand OTE Pathfinder rather than just read about it. In short: The OTE Pathfinder (for Optical Telescope Element Pathfinder), or James Webb Space Telescope Pathfinder, is a technology demonstrator and test article for the James Webb Space Telescope. It is a non-flight replica of the actual backplane, but only includes the center section, not the two "wings" on the side that extend and have additional segments on the actual JWST.

Key takeaways

OTE Pathfinder belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect OTE Pathfinder to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of OTE Pathfinder from memory before moving on to harder problems.

Reference excerpt

The OTE Pathfinder (for Optical Telescope Element Pathfinder), or James Webb Space Telescope Pathfinder, is a technology demonstrator and test article for the James Webb Space Telescope. It is a non-flight replica of the actual backplane, but only includes the center section, not the two "wings" on the side that extend and have additional segments on the actual JWST. It has been used for various tests and has some different configurations, but some of the major tests have been practicing installing mirror segments with non-flight hardware as well as thermal tests. The Pathfinder has also been tested in conjunction with flight hardware including the Aft Optics System. One of the goals and uses of the pathfinder is risk reduction for JWST program. The pathfinder allows practicing integration and testing procedures, and for risk mitigation With the Pathfinder it was possible to test phasing two mirrors together and also to do tests with the Aft Optical System. The OTE Pathfinder was part of the plan for integration and testing of JWST, and in particular supported the Optical Telescope Element (primary mirror, backplane, etc.). The OTE pathfinder uses two additional mirror segments and an additional secondary mirror, and puts together various structures to allow testing of various aspects of the section, including Ground Support Equipment. This supports the GSE's use on the JWST itself later on, and allows testing of mirror integration. OTE pathfinder has 12 rather than 18 cells compared to the full telescope, but it does include a test of the backplane structure. The pathfinder allowed practicing installing mirror segments with a non-flight mirror and non-flight backplane. Mirror installation is a task that necessitated practice due to the high-precision required. The Pathfinder backplane was completed in 2011. Three tests planned for the OTE Pathfinder were Optical Ground Support Equipment 1 (OGSE1), Optical Ground Support Equipment 2 (OGSE2), and Thermal Pathfinder. The Pathfinder was used with the Beam Image Analyzer (BIA) and another important related device is the AOS Source Plate Assembly (ASPA). ASPA provides infrared sources for doing optical testing.

California The flight-replica backplane was assembled in Redondo Beach, California, at the NASA contractor Northrop Grumman facility there. The flight backplane has two wings and a center section, whereas the pathfinder just as center section. The backplane was transported across country (see Continental United States) in a C-5 Galaxy transport aircraft to Joint Base Andrews, and to GSC by road. The section is contained with the Space Telescope Transporter for Air Road and Sea (STTARS), which was designed for the project. This facilitates hauling items around the country for different tests or assembly for the JWST project. The backplane is constructed out of graphite composite, titanium, and invar. Invar is an iron-nickel alloy with a low coefficient of thermal expansion (CTE or α), which means it does not significantly change size during temperature changes. One of the important features of the backplane is that it is thermally stable at low temperatures, because it is holding the main mirror, it must change size less than one-ten-thousandth of a human hair (32 nm) at −240 °C (−400 °F). Another test of the backplane design was the Backplane Structure Test Article, which was a one sixth portion of the full backplane.

Maryland (Goddard Spaceflight Center)

In 2014 the pathfinder was transported from California to Maryland. In Maryland it was used for practicing mirror installation at Goddard Space Flight Center. It arrived at GSC in Maryland in July 2014. Mirror segments were installed on the Pathfinder, which allowed the procedure to be practiced. At Goddard Spaceflight Center the two spare main mirror segments and a spare secondary mirror were installed on the pathfinder. The full James Webb Space Telescope main mirror has 18 segments (primary). It was considered to use silver, however gold is more durable than silver as a coating even though it is used for reflecting down to 400 nm wavelength light; JWST is primarily for 800 nm to 29000 nm. The Pathfinder weighed about 1,400 kilograms (3,000 lb) after the mirrors were installed.

Texas (Johnson Space Center) After the work done in Maryland at Goddard, the pathfinder was taken to Johnson Space Center in Texas, for cold environment testing. The Pathfinder was delivered to JSC by early February 2015. In preparation for its arrival, in 2014 Optical Ground Support Equipment was installed at the cryogenic test chamber at Johnson Space Center. The ground support equipment was tested during the OGSE-1 in Chamber A at JSC, after which the Aft Optical Subsystem and Beam analyzer were installed and tested in OGSE-2. The first test was completed by June 2015, and the second test was completed by November 2015. The third major test, which involves even more modifications to pathfinder is called Thermal Pathfinder. During the optical tests the mirrors had to be "phased" or aligned to a distance less than the wavelength of light, thousands of times smaller than the thickness of a human hair at a temperature hundreds of degree below zero.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with OTE Pathfinder

Start with the simplest possible case. Write down what OTE Pathfinder claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to OTE Pathfinder before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about OTE Pathfinder ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of OTE Pathfinder

In research: OTE Pathfinder appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses OTE Pathfinder in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: OTE Pathfinder is common in secondary-school and first-year university syllabi. It links to neighbouring topics James Webb Space Telescope, Technology demonstration spacecraft, so understanding it makes those chapters shorter.
In everyday life: Look for OTE Pathfinder outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study OTE Pathfinder in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what OTE Pathfinder means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain OTE Pathfinder out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is OTE Pathfinder in simple terms?

Why does OTE Pathfinder matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study OTE Pathfinder?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on OTE Pathfinder.